Qualidade do efluente de uma estação de tratamento de esgotos: confiabilidade Fuzzy

Abstract

In the present study we propose a Fuzzy Reliability Index (FRI) to evaluate effluent quality and performance of a wastewater treatment plant stations (WWTP) regarding to environmental regulations. The investigation was based on the concept of diffuse marginal function. For the methodological approach a full-scale treatment plan was selected. The Baldo WWTP was in Natal, Rio Grande do Norte State, Northeast Brazil (5° 47' 21.8" South; 35°12' 43.8" West, 7.0 m above the sea level), located in city of Natal, Rio Grande do Norte. The Baldo plant was in a 1.2-hectare area and treated a rate of flow of 22,000 m³/day but had capacity for to treat up 35,000 m³/day. The plant had the following configuration: two anaerobic units (UASB reactors), followed by anoxic chamber, aerobic reactors, secondary sedimentation tanks, and disinfection system. Data for the study comprised the regular monitoring of the Baldo WWTP from 2014 to 2017. Results showed the system reached good removal of organic matter and suspended solids (82.4, 77.5 and 79.3% for COD, BOD, TSS, respectively). The performance also was satisfactory for the removal of substances soluble in hexane (oil and grease) average of 77.8%. The average reductions in ammonia, total phosphorus wase 69.7 e 49.7%. For the case of thermotolerant coliforms the average removal was 5.064 units of Log10. The fuzzy approach was showed great potential for its simplicity and objectivity for diagnosis and evaluation of WWTP performance. Triangular fuzzy numbers (TFN) were applied, according to descriptive statistics data. The computation of diffuse reliability index considered individual and aggregated values. The index considered additive approach based in the average weighted of the individual FRI.